This invention concerns a contact lens, particularly well suited for observation of the eye and its treatment by a coherent radiation optical beam.
Different eye diseases, like, for example, certain glaucomas, cataract or even disorders resulting from the presence of membranes can necessitate, for their operation or the preparation of that operation, the use of a laser beam of very high energy density in certain regions of the eye. For that purpose, ophthalmologic treatment units of the type described in the European patent application published under No. 0 030 210 in the assignee's name herein are used. Those units make it possible to direct a laser beam toward the eye consisting usually of very short but very high-intensity pulses delivered, for example, by an Nd-YAG laser operating on Q-Switch mode. The width of the beam exiting from the unit is in the order of 16.degree..
One can, of course, envisage directing that beam straight to the eye without using a contact lens, notably, in order to reach the iris or the vicinity of the crystalline surface by a firing in a direction parallel to the axis of the eye. The narrowness of the beam then guarantees slight width aberrations on entering the eye but also gives rise to numerous disadvantages. In particular, the risks of reaching zones other than the one really aimed at are increased, with the localization of the optical click phenomenon taken advantage of to treat this zone being less fine. The focusing spot of the beam on the target is also larger.
There are various contact lenses that can be used. Three shall be identified.
The Goldmann type lenses are made in one piece, usually of an organic material, e.g., acrylic, and they have a plane or very slightly spherical entry surface. Originally, they were provided essentially for examination of the fundus of the eye, but they are also used for interventions in the anterior chamber of the eye. Those contact lenses do not solve the problems associated with the width of the beam, but such lenses lessen the problems with respect to the previous solution. Furthermore, these lenses introduce marked aberrations at the entry face. Their essential advantage is to assure very good reliability and the patient's comfort at the contact lens-eye interface due to the very good surface state that can be obtained with the materials used. That surface state prevents the formation of microclicks at that interface. On the other hand, the addition to the entry surface of an anti-reflecting coating for the wavelengths of the treatment beam (1.06.mu. for the Nd-YAG laser) and in the visible range presents difficulties not yet mastered.
The Abraham type lenses consist of a mineral glass entry lens coupled eccentrically with a Goldmann type contact lens. Those lenses, usable for iridectomy alone, make it possible to widen the treatment beam, which enhances its better focusing. Furthermore, the entry face can be easily treated. However, added to the aberrations at the entry surface is a coma aberration in the eye entry diopter due to the conjugate effect of a greater width and an off-centering of the lens.
The Roussel type lenses more recently developed and described, for example, in European Patent Application No. 82 810 044.6 in the assignee's name herein are made in one piece of mineral glass and contain a mirror-forming side face. The spherical entry surface forms a wave surface for the incident beam, the width of which is not modified. The essential advantage of these lenses is to enable the aberrations to be considerably reduced because of their better geometry. They are, furthermore, not very sensitive to rotations of the lens. On the other hand, their use is relatively difficult due to the presence of the mirror. The inclination of the treatment beam in relation to the axis of the eye, furthermore, diminishes firing efficiency. Finally, by reason of the interface problems already explained above, they do not guarantee optimum reliability at the mineral glass-cornea junction.